This invention relates to a motorcycle frame and more particularly to an improved, welded-up frame assembly for a motorcycle that provides a more rigid structure for mounting of the rear wheel of a motorcycle.
As is well known, motorcycles generally include a frame assembly that is made up of a welded-up construction. The typical frame construction includes a headpipe at the front of the frame and which dirigibly supports the front wheel via a steerable front fork assembly. From this headpipe, there extends generally rearwardly and in somewhat downward fashion one or more main tubes. In addition, down tubes also are affixed at their forward ends to this headpipe and extend downwardly and rearwardly. At the rear ends, the main tubes and down pipes are joined, frequently by a bracket assembly. This bracket assembly provides a support for the rear wheel and/or the rear wheel suspension mechanism. Although the shape of the individual frame members may vary, the described construction generally is the type utilized on the great majority of the motorcycles.
In addition to supporting the front and rear wheels, the frame assembly must also provide the space for the powering internal combustion engine and the transmission and drive arrangement for driving the rear wheel. The open type of frame construction generally employed is desirable because it offers easy access to the various mechanical components of the motorcycle for servicing and/or replacement.
Although the type of structure described is generally serviceable and satisfactory, the positioning of the rear wheel support at the extreme rear end of the frame gives rise to certain undesirable structural features. First, the loading of the frame members, because of this construction, is such that there are substantial bending and/or shearing forces exerted on the frame members. It is obviously particularly desirable to load the frame members primarily in tension or compression.
In addition, this rearward positioning of the suspension point results in the difficulty in providing large suspension travels, if the rear wheel is supported for suspension movement relative to the frame. Trailing arm constructions are generally employed for this purpose, and if the trailing arm has a pivotal point at the rear end of the frame, then the wheelbase of the bike becomes elongated considerably in order to provide a long trailing arm. This is not particularly desirable from a ride standpoint.
It is, therefore, a principal object of this invention to provide an improved and compact frame assembly for a motorcycle.
It is a further object of this invention to provide a generally built-up type of frame assembly wherein the rear wheel suspension and frame cooperate in such a way so as to minimize bending loading on the frame members and to, at the same time, permit a large suspension travel while maintaining a manageable wheelbase.
It is a further object of this invention to provide an improved high-strength frame assembly that nevertheless is compact in construction and facilitates the ease of servicing of the components of the motorcycle carried by the frame.